The present invention concerns a safety device for a front-loading weapon, commonly called a “mortar,” which launches projectiles in a high trajectory. The mortar comprises a relatively short barrel having a closed breech end, attached to a breech block forming a base, and an opposite open end, aimed upward, for ejecting the projectile. The mortar is loaded by inserting self-propelled projectiles into the open end of the barrel. Each round is inserted, front end forward, and falls backward inside the barrel. At the breech end of the barrel the projectile is automatically ignited by a firing pin and propelled forward by the propulsive gases emitted from its tail end.
While such an weapon is relatively simple and easy to use, it has been the source of frequent and serious accidents resulting in the loss of life and limb to the attending soldiers, called “mortar men.” Such accidents arise from a dangerous combination of circumstances, such as misfires, hang-fires (failure to fire right away) and double loading of the mortar rounds, that lead to inadvertent detonation of this ammunition.
Modern mortars are capable of high rates of fire (up to 30 rounds for the first one or two minutes of fire). Mortar men are trained to detect hang fires, but in the frenzy of firing, hang fires and misfires can go undetected with catastrophic results.
The chart below is a short list of known accidents associated with a mortar crew inadvertently double loading a mortar. This situation can easily occur when (1) the mortar has a “low order” event, (2) the mortar crew is rushed and does not observe proper firing, and/or (3) the mortar suffers a hang-fire and the crew is unaware that a mortar round did not fire and exit the barrel before a new round was inserted.
Unit/MortarCasualtiesProbableLocationYearTypeKilledWoundedCauseUS Marines201360 mm78Double(Nevada)loading andHang FireRomanian2010Unspeci-33DoubleArmyfiedloadingBritish198281 mm32DoubleArmyloadingUS Army200681 mm14Double(Hawaii)loadingUkrainian2008120 mm 13DoubleArmyloadingFinnish2005120 mm 15DoubleArmyloadingTotal164056 Casualties
Some attempts have been made to address this situation by providing ways to prevent double loading in mortars. One important reference is the U.S. Pat. No. 5,965,835 to Karl Gartz entitled “Apparatus for Monitoring the Loaded or Unloaded Condition of a Front Loading Weapon.” This patent discloses a mortar safety device that employs an array of acoustic sensors located inside the barrel and in the breech block. The sensors are piezoelectric devices tuned to measure characteristic vibrations of the round impacting the firing pin, in particular the reaction of the base plate as well as oscillations of the barrel. A filter is used to collect only those signals from such sensors that are compatible with the impact of the round on the firing pin. After processing these signals, information provided by the electronic controller is used to turn on an alert lamp and/or a mechanical device in the muzzle that prevents further loading.
The fact that the sensors are located inside the barrel is a serious drawback of this system because it is not easy retrofit this equipment to existing mortars. The patent fails to teach how the sensors are to be installed, nor does it describe in detail how the tuning is realized.
The U.S. Pat. No. 3,698,282 of Zigmund Albatys, issued Oct. 17, 1972, and entitled “Mortar Safety Device for Preventing Double Loading” describes a purely mechanical device that prevents loading of a mortar round if the barrel has not been cleared by firing a previously loaded projectile. A mechanism located in the muzzle uses a series of arms and locking devices to block the loading of a fresh round until the prior round is fired. This mechanical device returns to its initial position once the barrel is cleared so that a new round can be loaded into the weapon.